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Brake Hub Analysis Of Cracking Failure
- Oct 30, 2017 -

Brake hub also known as brake drum or brake pot is a brake hub, is based on the friction between the two, with friction to reduce the wheel rotation speed of the brake device. The working principle of the brake drum is to rely on the braking device which produces friction and reduces the wheel rotation speed by friction. When you step on the brake pedal, the force of the foot will push the total pump in the brake forward and create pressure in the oil circuit.

The advantages of the brake hub

1. With automatic braking, the brake system can use a lower oil pressure, or a brake hub with a much smaller diameter than a brake disc.

2. Easy to install the hand brake mechanism. Some rear-wheel-mounted brake-type models will be fitted with a hub-brake braking mechanism at the center of the brake disc.

3. Parts processing and composition is relatively simple, and has a relatively low cost of manufacturing.

Disadvantages of the brake hub

1. Drum brake Drum in the heat after the diameter will increase, and caused by stepping on the brake pedal increase, prone to brake reaction is not as expected. As a result, when driving a car with a drum brake, it is necessary to avoid a continuous brake resulting in heat decay due to high temperature.

2. The braking system reacts slowly, the pedal strength of the brakes is more difficult to control, and is not conducive to the high frequency braking action.

3. The construction of complex parts, brake clearance must be adjusted to make maintenance difficult.

Cracking Failure Analysis:

Brake Yi in the braking process due to dry friction and friction is large, often appear overheating redness, at this time staff often to brake Yi bu water to reduce its temperature. The brake Yi is constantly rubbing heat to make its surface temperature rise. When its table and color is fuchsia, the surface local temperature can reach 800 ℃ above, already can cause the organization structure change and plastic deformation. Using tap water to reduce the temperature of the brake Yi, the foot has played a quenching effect, so that the surface local hardness increased, internal stress increased, cold brittleness enhanced. At the same time, due to the repeated action of tangential force, the crack propagation in the block carbides and inclusions at the surface layer is accelerated with the effect of irregular alternating impact force.

The Brake-yi organization is mostly in a casting state, coarse grains, there are many inclusions along the crack point distribution near the crack, at the same time at the crack and the grain size is very uneven, these tissue defects to a large extent reduce the strength of the material and Xiang, easy to cause stress concentration. The original heat treatment of the workpiece using the positive fire + intermediate frequency induction heating quenching and self tempering. From the analysis of the Organization, there are problems in the normalizing process: ① heating temperature and heat preservation time are not enough, the casting structure of a considerable part is retained, and the ② temperature uniformity is poor, so the organization is uneven. Because of the large size of the brake, normalizing heating is carried out in the coal-fired furnace, the temperature uniformity is poor. The original process indicated that the thermal insulation temperature is (850~900) ℃, and in fact the temperature of the thermocouple indicated is difficult temperature, so the actual normalizing temperature is lower than the temperature of the process requirements. In comprehensive analysis, the brake Yi produced crack failure is mainly due to the temperature is not enough, most of the organization is still in the casting state, coarse grain, the workpiece strength is low, and there are local inclusions. In addition, the working condition of the workpiece is very bad, often occurs the hot and cold phenomenon, the internal stress is big, thus causes the workpiece to form the crack source from the inclusions, and gradually expands the crack.